onspeed

almost a year ago now, my 951 left me stranded at a stoplight. It did not stall, but the idle suddently got really rough, and car was having trouble revving. Was not drivable, had to push it into the gas station and call the tow truck. I've since left it in the garage, always putting off fixing it. My other car, camaro, recently spun a rod bearing, so i had to decide if i wanted to fix the porsche or the camaro. Porsche had that engine problem, plus needed a clutch kit... pilot bearing or TOB or something was broke. I was thinking the engine problem was due to bad vacuum lines, however i just replaced them today with the lindsey set, and it did not solve my problem. Here's some info on the car. '86 951, 45,000 - new head gasket, oil cooler gasket, FPR, dampener, vacuum hoses, ignition coil, spark plug wires, cap and rotor (i think, will check them tomorrow), tps, possibly a few other small things here and there. I have a video in my old thread, i think the car is running super rich or something. Bypassing ISV via jumpers did not help the idle, nor did disconnecting the o2 sensor.

Things I plan to check: make sure all 4 injectors are working, DME solder joints, AFM, speed/refernece sensors.

I know the speed and reference sensors are in the clutch housing, is it possible for transmission issues to damage them? Anyone have other suggestions? I already have the clutch kit and hardware kit, so it's too late to turn back now. Need to get the engine running properly before starting the daunting clutch job. I think the car was running a little on the hot side before it broke, had it idling for a bit to see if my fans were working properly (i don't think they were, i engaged the AC to kick them on.)

Adam Poland

Sounds like a problem I had. Mine was a cracked intercooler-->hard pipe boot, and the tps needed adjustment. I doubt its the sensors, because I dont think your car would start at all had that been it. I dont have enough knowledge on the sensors to know if that is valid or not though lol. I would check them anyway.

onspeed

cracked intercooler? I'll put that on my list of things to check... and i'll recheck to make sure my TPS is adjusted right.

Adam Poland

It was the rubber boots between the intercooler and hard pipe lol. Not the intercooler itself. It wouldnt hurt to check the entire intake system for cracks either. You never know.

JohnKoaWood

Does it run better with the TPS disconnected?

Your rotor button is also a good thing to check. If the small bolt holding it on has gotten loose it can cause a no start, hard idle, bad off idle running.

also try to cause a vacuum leak and see if it changes... the IC pipe couplers are a good place to look...

onspeed

runs the same with the TPS disconnected. will check cap and rotor tomorrow after work, also try to induce vacuum leak and report back.

will bad relays cause any similar symptoms?

onspeed

changed out the couplers and piping leading to/from the intercooler, no change.

one thing i tried though, i removed the hose that inserts on the left side of the pipe that runs from the IC to the Turbo. it runs down to under the intake... venturi hose maybe? anyhow, when i used a cork or my finger to plug the hole on the pipe, and left the line open (it's a vacuum line) the car seemed to run better. not perfect, but definitely smoother than it is now. maybe that tells us something?

upon start up, the car sounds like it's cammed or something. it smooths out a little bit, but definitely does not sound like normal.

Adam Poland

Idle stabilizer valve? I have mine removed, and it sounds like my car has a nasty cam until it warms up and gets driven. A venturi delete is a great investment if you ask me.

onspeed

yes, i just connected the dots in my head. i'm not sure how the ISV works, but i think i read in my other thread that if it's stuck open, then it would basically be venting vacuum to the atmosphere. so i'm assuming either the venturi lines are cracked, or the ISV is stuck, meaning when the air which goes through the hardpipe>ISV line, is eventually vented to the atmosphere instead of being in a closed circuit, as i assume it's supposed to be. in short, a big vacuum leak?

it makes more sense in my head. when i plug the hole, the air doesn't go down that pipe, meaning more air into the intake, and it starts to run right. so my problem is too much gas, but too little air.

edit- one thing i noticed is that the car will die if i plug the hardpipe>isv line. this normal? and is the "cycling valve" the same as the ISV?

Adam Poland

The cycling valve is the factory boost controller. Mine split in half and I had no boost limit, which in turn blew my motor. What youre saying about the big vacuum leak makes complete sense. To inspect all of those vacuum lines under the intake, you have to remove the intake manifold (if you havent done so already). If they are all original, they could be dry rotted and cracked. If that is the case, a venturi delete from Lindsey Racing will delete all of that crap underneath the intake. If I'm not mistaken though, you have to buy a manual boost controller to replace the cycling valve, since it will no longer be plugged up. It really all depends on which route you want to go. But I would strongly recommend taking your manifold off and inspecting all of the hoses thoroughly, before making any hasty decisions on what to do.

onspeed

Just removed the intake, took out the isv, looked clean, but sprayed it down with carb cleaner anyways. am i supposed to bend the metal tabs that keep the casing on and spray in inside as well? or just through the pipe ports?

also, to test for leaks in my tube, i was just stuffing one end and blowing through the other. they seem to be fine, however i blew through one tube a small metal thing fell out. some sort of flow reducer? a small cylindrical piece of metal with a small hole through the center. and the line is double clamped, so i assume it's supposed to be in there?

the very center pipe connecting the two metal metal tubes. see where it has a clamp in the middle?

Adam Poland

Hmm....I dont remember seeing that extra clamp on my car. I've never heard of any flow reducers or anything like that before. As for the ISV, you may want to see if someone else can answer that. I never sprayed mine down, so I dont know what is ok to spray and whats not ok to spray. Just being honest to avoid causing you any more trouble lol. It is very weird that your car just randomly did this...

onspeed

okay, going to try deleting the ISV for now, and see if that'll fix my issues.

edit- tried to ghetto rig a ISV bypass... instead of plugging the pipes, i simply plugged the hoses. Used a cork for the hardpipe hose, cork for the ISV > Intake hose, and then a sparkplug for the Y piece on the brake booster>intake hose. I don't have venturi delete pipes. I'm not sure it worked as i intended. car would NOT start without giving some gas, and would die if i let go. tried loosneing the idle control screw by 2 and a half circles... no help there. also was a LOT of smoke as i held the gas down a bit. i think my make-shift isv delete is probably the culprit. will have to bench test the ISV tomorrow using a 12v and hope it's my problem. looks promising though.

Adam Poland

It's very possible that it could be. If you have any spare tubing, bypass your ISV that way. By corking it off and plugging things up, something may have been messed up. You never know with a 944 turbo lol. They practically run off of vaccuum. I've deleted every vaccuum line I can. All I have now is the venturi delete, the hose from the BOV to the intake, and that is teed into the FPR. So in total I have 4 vaccuum lines. lol

CDH-CTT

onspeed,

DId you ever check your Vane air flow meter?( I read though the other post and didnt see anything about it.) It can fail over RICH and the car will idle very rough and not start. I had mine go out but it was going lean and watching my A/F gauge I could see it drop off then the car would die and not restart until I replaced it with a donor one I borrowed. I know that there is a way to check the resistance also if you pull the black cover off and use a analog volt meter connected to the pins and then sweep the plate slowly and see if it has dead spots....also look for burn marks on the contact points....

Carl